Open projects and solutions
When opening a .NET solution, Rider will automatically restore all NuGet packages in each project and will also detect the list of target .NET frameworks in each project. If there are multiple target frameworks, you will be able to change the active framework in editor breadcrumbs.
Open solution from welcome screen
When you start JetBrains Rider for the first time, a welcome screen appears where you can click Open and choose your solution.
On each subsequent start, JetBrains Rider automatically opens the solution you worked with in the previous session. If you want to change this behavior, clear the Reopen projects on startup checkbox on the Appearance & Behavior | System Settings page of settings Ctrl+Alt+S — this will enable the welcome screen to appear on each startup. When the welcome screen is enabled, all solutions that you worked with are listed in the right pane. You can search the list in case you have a lot of solutions — just start typing the solution name, and a search field will appear.
Switch to another solution
Press Ctrl+Shift+O or choose from the menu.
Choose any of the recently opened solutions from the list under .
If you have several solutions in the same directory and one of them is open, you can switch to the File System view in the Explorer window to see all other .sln and .slnf files in the directory. You can then right-click the desired solution file and choose Open Solution:
Rider allows opening several solutions simultaneously in different windows. By default, each time you open a solution while another one is opened, it prompts you to choose whether to open the project in the same window or in a new window. If necessary, you can set the default way of opening projects on the page of JetBrains Rider settings Ctrl+Alt+S.
On macOS, you can merge several opened solution windows into one window, where each solution will have its own tab. To do so, select from the main menu. To restore separate windows, drag tabs outside the application window frame.
Different ways to open solutions
When you click Open on the welcome page or choose from the menu, the Select Path dialog opens where you can choose the solution in different ways:
Choose either a solution file (.sln)
Choose a project file (for example, .csproj) — in this case Rider will generate an .sln file if necessary.
Choose a folder — in this case, you will be able to choose any of the solution files located in the selected folder or in any of its subfolders.
If your solution is directory-based, that is all its projects are arranged in subfolders without the .sln file, you can choose the root folder in the Select Path dialog to open all projects from subfolders, for example:
RootFolder ├── Project1 ├── Project1.csproj ├── [project contents] ├── Project2 ├── Project2.csproj ├── [project contents]Note that whenever you choose a folder in the Select Path dialog, you can always opt for opening it as a folder (as opposed to a .NET project). In this case you will be able to browse all files in this folder but code analysis and other features will not be available in .NET files (*.cs, *.vb, and so on).
Open a solution from a version control system
Rider also allows opening solutions from different version control systems. It can, for example, log in to GitHub, and clone a repo to the local file system. Once done, it will prompt you to choose a solution to open from those available in the repo.
To clone a repository, you can select from the menu or click Get from VCS on the welcome screen.
Manage recent solutions
Each time you open a new solution, JetBrains Rider saves it in its history and lets you quickly reopen it from the menu.
To configure the list of recent solutions, choose from the main menu. In the popup that opens, you can click the 
icon next to a solution and choose one of the actions:
To remove a solution from the list of recent ones, you can also select it using the Up and Down keys, and then press Delete.